1. Field of the Invention
The invention concerns a method of measuring the flowrate of fluidized powder in a circuit including an air-powder mixture drive area into which air is injected.
The invention enables evaluation of the powder mass flowrate on the basis of measurements at selected points of a mixture drive device defining said drive area. It also enables flowrate regulation, reporting of absence of powder and determination of the degree of wear of an essential component of the drive device which is also part of the powder flowrate measuring means.
The invention also concerns a powder flowrate measuring device implementing the above method.
2. Description of the Prior Art
U.S. Pat. No. 4,480,947 describes a powder flowrate measuring device disposed between a fluidized powder storage tank and a powder conveyor device forming a sort of compressed air pump whose function is to impart to the air-powder mixture sufficient energy to enable it to be conveyed in a pipe to a station where it is used. The measurement principle employed is to inject air at a constant flowrate into a pipe section of predetermined length and cross-section and to measure the pressure drop across this pipe section. The only function of the air injected is to move the powder across the orifice at a predetermined speed. In other words, a head loss is generated only to measure the mass flowrate of powder. Generating this head loss disturbs the operation of the powder conveyor device further downstream. Also, the accuracy if the measurement is reduced over a period of time because of wear of the pipe section in which the head loss is produced. The degree of wear becomes unacceptable after a varying period of time dependent on the operating conditions. The device described comprises no means of evaluating this wear. Finally, the construction of the known system is highly complex because it requires a controlled flowrate compressed air supply and a dedicated arrangement for generating and measuring the head loss.
The invention proposes to use another type of measurement which is free of the drawbacks mentioned above and employs only a limited number of sensors in a particularly simple arrangement.